Re: IIgs MB repair info

["Mark Cummings" <NOTfigjams@primus.com.au>]

"Ed Eastman" <noone@nowhere.net> wrote in message
3F0C7AEF.3020002@nowhere.net">news:3F0C7AEF.3020002@nowhere.net...
> OK, this sounds like the CPU is not functioning.  LAst time I saw this
> problem was when someone yanked the accelerator out and forgot to put a
> CPU in.

he did say that ALL socketed chips tested OK, so they problem must lay
elsewhere.

I have fixed one ROM-3 which would not boot, no legible text on the screen.
when I hit ctrl-reset I did get some reaction but still garbage on the
screen.
the cause was just 1 bad DRAM chip in the 1MB RAM area. I think there are
about 12 RAM chips on the ROM-3 boards altogether, and I got to #9 or #10
before I found the culprit, which pixxed me off somewhat :( although I
quickly changed my tune when I realised that I now had myself a ROM-3 :)

BTW due to the difficulty of removing the chips, I only removed one at a
time to minimise potential damage to the board. the smaller 4164 DRAMs were
tested in a socketed //e. I used the System Test (Ctrl-SA-Reset) sequence to
proove they worked. the larger 511000 DRAMS were tested in a socketed GS-RAM
expansion card in another GS. a test program was used to test the DRAMs.

replacement DRAM was obtained from a old PC video card. those ISA slot types
that contain only 256K or 512K of RAM are good candidates for spares DRAMs
for the GS.

the thing that I find amusing, for both the GS and //e is that the built in
test routines that test RAM (among other things), are a complete waste of
time/space becuase I have found that if the RAM is faulty the tests won't
even run. I guess this could depend on how they go faulty, but for me 2 out
of 2 failed DRAMs basically locked up the machines they were in.

Mark